Spectroscopic analysis, including absorption spectroscopy and fluorescence spectroscopy, may be used to identify and measure or quantitate various types of suspended and dissolved organic and/or inorganic materials or compounds present within a sample. These types of analyses have a wide variety of applications in chemistry, food science, biology, pharmacology, materials/nanotechnology, and water quality analysis in various environmental, geology, hydrology, oceanography/limnology, and soil science applications, for example. Spectrophotometric measurements may be used to detect and quantitate compounds that include chromophores that absorb light in the visible-ultraviolet (VIS-UV) range having wavelengths of between about 700-200 nm, respectively, for example. The amount of light energy absorbed generally varies with the concentration of the compound and the distance traveled through the compound. Likewise, some compounds can be identified and quantitated based on characteristic fluorescence associated with colored or chromophoric matter, i.e. absorption of shorter wavelength excitation light energy and re-emission of longer wavelength (and lower energy) emission light energy.
Absorption and fluorescence spectroscopy have been used in water quality analysis applications to identify and measure colored or chromophoric dissolved organic matter (CDOM), which may include various types of compounds, such as humic and fulvic acids, chlorophylls, proteins and amino acids, nucleic acids, sewerage, bacteria, fertilizers, pesticides, etc. One prior art strategy is to perform separate fluorescence and absorbance measurements using corresponding instruments. The resulting data may be correlated and/or corrected using various commercially available software applications. However, separate measurements require transfer of the sample and data for desired analyses and fluorescence spectral corrections. In addition, fluorometers that use scanning excitation and emission monochromators having single channel detectors (typically photomultiplier tubes (PMT's)) often have scanning times of 30-90 minutes or more and may not accurately detect and quantitate unstable compounds that can degrade over time and/or with exposure to the excitation light. Similarly, the accuracy of results obtained using such long scanning times may be adversely affected by time-dependent changes in dissolved gases, pH, aggregation, sedimentation, and other chemical processes. Long scanning times combined with relatively limited Raman signal-to-noise ratios may provide uncertainty and statistical inaccuracy of the coordinated absorbance and fluorescence readings.
To address some of the above issues, commercially available fluorescence instruments have been developed to facilitate parallel fluorescence and absorbance readings. However, even this approach does not provide near simultaneous collection of absorbance and emission data for fluorescence reabsorbance correction. In addition, general purpose instruments may have various design compromises to accommodate both absorbance and fluorescence measurements.